No idea if there are any UK stockists, but I would say that trying on before you buy IS essential with Lundhags.
The size guide on their site was a size off (too small) when I came to trying pairs on, and different models of the same size fitted while others didn't.
It also helps to try on using different sock combinations. I have a few pairs of Lundhags and the best are the basic shell/unlined models. I can wear them with a heavyweight sock with room for another pair of socks if needs be.
Very good (and expensive) boots, but I would rate these boots from Jörn as being just as good if not better.
The M96 Model would be a Lundhags equivalent and they run truer to size:
http://www.jjensen.no/stovler.html